Geotechnical Engineering

DHARM

CAISSONS AND WELL FOUNDATIONS 785

∴ P =

N

(sin cos)μθ θ+

Here N = vertical force on the curb

θ = angle made by the bevel edge with the horizontal.

Resolving horizontally,

P sin θ – μ P cos θ = H

where H = horizontal force on the curb.

H = P(sin θ – μ cos θ)

Substituting for P,

H =

N(sin cos )

(sin cos)

θμ θ

μθ θ

+

+

Hoop tension, T = H

×D^1

2

= 05. 1

sin cos

sin cos

ND

θμ θ

μθ θ

−

+

F

HG

I

KJ

...(Eq. 19.17)

D 1 = centre to centre of steining walls
Suitable reinforcement should be provided to resist the hoop tension developed.
Sometimes, sand blow may cause sudden sinking of the well and a consequent spurt in
hoop tension. To account for such a contingency, the hoop tension reinforcement is increased
by 50%.

When the cutting edge is not able to move downward due to the reaction developed at
the curb and the bottom plug, the conditions will be as shown in Fig. 19.14.

The hoop tension developed is given by

T =

qD

r

D

82

1

2

RS| .. 1

T|

U

V

|

W|

...(Eq. 19.18)

D

b

D 1

r

p 2

p 1

q

Fig. 19.14 Inverted arch of cutting edge